The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus and methods for the localized delivery of therapeutic vibratory energy within the vasculature and other body lumens.
Despite the growing sophistication of medical technology, vascular (blood vessel) diseases, such as acute myocardial infarction (heart attack) and peripheral arterial thrombosis (blood clots in leg arteries), remain a frequent, costly, and very serious problem in health care. Current methods of treatment, often expensive, are not always effective. In the U.S. alone, the cost of treatment and support and the loss of productivity due to vascular diseases together exceed $40 billion per year.
The core of the problem is that diseased sites within the blood vessels narrow and eventually become completely blocked as a result of the deposition of fatty materials, cellular debris, calcium, and/or blood clots, thereby blocking the vital flow of blood. Current treatments include drugs, interventional devices, and/or bypass surgery. High doses of thrombolytics (clot-dissolving drugs) are frequently used in an effort to dissolve the blood clots. Even with such aggressive therapy, thrombolytics fail to restore blood flow in the affected vessel in about 30% of patients. In addition, these drugs can also dissolve beneficial clots or injure healthy tissue causing potentially fatal bleeding complications.
While a variety of interventional devices are available, including angioplasty, atherectomy, and laser ablation catheters, the use of such devices to remove obstructing deposits may leave behind a wound that heals by forming a scar. The scar itself may eventually become a serious obstruction in the blood vessel (a process known as restenosis). Also, diseased blood vessels being treated with interventional devices sometimes develop vasoconstriction (elastic recoil), a process by which spasms or abrupt reclosures of the vessel occur, thereby restricting the flow of blood and necessitating further intervention. Approximately 40% of treated patients require additional treatment for restenosis resulting from scar formation occurring over a relatively long period, typically 4 to 12 months, while approximately 1-in-20 patients require treatment for vasoconstriction, which typically occurs from 4 to 72 hours after the initial treatment.
Bypass surgery can redirect blood around the obstructed artery resulting in improved blood flow. However, the resulting bypass grafts can themselves develop scar tissue and new blood clots in five to ten years resulting in blockage and the need for further treatment. In summary, all current therapies have limited long term success.
The use of ultrasonic energy has been proposed both to mechanically disrupt clot and to enhance the intravascular delivery of drugs to dissolve clot and inhibit restenosis. Ultrasonic energy may be delivered intravascularly using specialized catheters having an ultrasonically vibrating surface at or near their distal ends. One type of ultrasonic catheter employs a wire or other axial transmission element to deliver energy from an ultrasonic energy vibration source located outside the patient, through the catheter, and to the ultrasonically vibrating surface. While such systems can deliver relatively large amounts of energy, the need to transmit that energy through the entire length of the catheter presents a substantial risk to the patient.
Moreover, such catheters are typically rigid and cannot easily traverse narrow, tortuous arteries, such as the coronary arteries which frequently need to be treated. Because of their rigidity and inability to follow the vascular lumen, these catheters present a serious risk of vascular wall perforation.
In order to avoid the use of ultrasonic transmission members, catheters having ultrasonic transducers mounted directly on their distal ends have also been proposed. See, for example, U.S. Pat. Nos. 5,362,309; 5,318,014; 5,315,998; 5,269,291; and 5,197,946. By providing the transducer within the catheter itself, there is no need to employ a transmission element along the entire length of the catheter. While such catheter designs offer enhanced safety, they suffer from a limited ability to generate large amounts of ultrasonic energy. Even though certain of these designs, such as that described in U.S. Pat. No. 5,362,309, employ "amplifiers" which enhance the delivery of ultrasonic energy, such designs are still problematic. In particular, the catheters of the '309 patent have relatively long, rigid transducers and are not amenable to receiving guidewires, both of which features make it difficult to position the catheters within the vasculature, particularly the coronary vasculature.
For these reasons, it would be desirable to provide improved energy-transmitting catheter designs which overcome at least some of the problems discussed above. In particular, it would be desirable to provide catheters having vibratory energy transducers at their distal ends, where the transducers are capable of oscillating interface surfaces with relatively high energy and amplitude. Additionally, it would be desirable to provide vibratory drivers which are capable of driving interface surfaces directly or in combination with resonant assemblies which amplify the displacement of the interface surface. It would further be desirable to provide transducer and driver designs which are highly efficient in order to minimize the production of heat within the vascular or other luminal environment. It would be still further desirable to provide methods for the intraluminal delivery of ultrasonic energy, where the ultrasonic energy is useful for a variety of purposes, including the direct mechanical disruption of clot, the enhancement of thrombolytic activity of agents to dissolve clot, and the enhancement of pharmacologic activity of agents to prevent restenosis of vascular sites previously treated by angioplasty or other interventional methods.